Water electrolysis with bases
To carry out the electrolysis of water in a basic environment and observe the different reactions.
What students learn
The science behind this experiment
This experiment shows the electrolysis of water using a different redox reaction. By changing the pH of the solution the reactions differ, although the results are the same.
In the basic environment there are OH – ions and Na+ ions, which migrate respectively towards the anode and cathode.
At the cathode, water molecules are reduced because their potential ( E0( H2O / H2 ) = – 0.83 V ) is greater than that of the sodium ions ( E0(Na / Na+ ) = – 2.73V ).Sodium ions will not undergo any reduction due to their very negative reduction potential.
At the anode OH – ions are oxidised because their potential (E0( O2 / OH ) = + 0.40 V) is lower than the potential of the redox couple ( E0( O2 / H2O ) = +1.23 v).
At the cathode (–) 4 H2O + 4 e – → 2 H2 + 4 OH –.
At the anode (+) 4 OH – → O2 + 2H2O + 4 e –.
Equipment used
- U tube with side outlets — 1276.10
- Platinum electrodes — 4716.12
- Connecting wires, red — 2522.03-04
- Connecting wires, black — 2522.04-08
- DC power supply
Chemicals and reagents
- Sodium hydroxide 0.2 M — R:35 S:26-37/39-45
Safety notes
- Always wear protective goggles and gloves.
- Hydrogen and air mixtures are explosive. Make sure there are no naked flames near the apparatus.
Questions for students
- Describe what happens in the apparatus.
- Write the balanced equations of the process and record your observations.
- What happens on igniting the test tubes? State where hydrogen and oxygen are produced.
- What are the differences between electrolysis in a basic and an acidic environment?
What to expect
<p>Passage of the electric current causes bubbling at the electrodes.</p><p>The gas collected at the cathode () pops stating the presence of hydrogen.</p><p>The gas collected at the anode (+) brighten up the flame indicating the presence of oxygen.</p><p>The reactions in the basic environment involve OH – ions instead of H+.</p><p>At the cathode () water molecules are reduced producing OH– and hydrogen. At the anode (+) OH – ions are oxidised to oxygen and water.</p>
Disposal
Dispose of the solution into the waste container.
Run this experiment in your classroom
This experiment is part of the ATP Mobile Lab — a self-contained laboratory that turns an ordinary classroom into a working science lab, with over 200 experiments in physics, chemistry, biology, robotics and engineering. Gali, the AI tutor built into ATP Connect, guides students through each step and answers their questions at the bench.
See the Mobile LabTalk to our team